I am not a tech person, but I cleaned out my secondhand PC today, and it took hours with the sheer amount of dust accumulation. The fans were nearly overloaded with it!!
Does a clean PC run better / faster than one filled with dust? Or is it more a matter of keeping the fans running easily? Or something else…? Idk, maybe I imagined it, but it seemed to boot much faster after cleaning. Could be wishful thinking!
On top of that modern computers are essentially designed to run as fast as they possibly can while staying just under their max temperature. Especially laptops, they will regularly kiss 100c as part of turbo boost.
Your GPU has a much lower temperature limit and starts throttling way sooner than its max rated temp since they do NOT like running hot. Your CPU will tolerate it, but your GPU is far too large of a chip for this temperature fluctuations.